Multiple cardiopulmonary diseases result in tissue hypoxia, which is a deficiency of molecular oxygen available for cellular metabolism. Conditions such as influenza, asthma, pneumonia, and the adult respiratory distress syndrome are examples of diseases which may produce tissue hypoxia because of complex pathology within the lung. Treatment of hypoxia is conventionally directed at the cause of hypoxia. For example, when hypoxia is caused by deficiencies in the partial pressure of oxygen in inspired gas diffusing across the alveolar capillary membrane in the lung, conventional treatment involves increasing the partial pressure of inspired oxygen in the inspired atmosphere.
Increasing the partial pressure of inspired oxygen may be accomplished via multiple breathing devices such as masks, nasal cannula, endotracheal tubes, tracheostomy tubes, mechanical ventilators. In essence, the purpose of oxygen inhalation is to increase the quantity of oxygen absorbed into the blood in hopes of improving oxygen delivery to cells and tissues. Traditional methods of oxygen therapy involve the inhalation of gaseous oxygen. These methods, however, are associated with several complications and limitations. First, if the breathing passages are blocked or if a person has stopped breathing altogether, inadequate amounts of oxygen are absorbed into the bloodstream to sustain cellular metabolism. Second, gaseous oxygen inhalation may be toxic to tissues if inhaled in high concentrations over prolonged periods. Third, inhalation of high concentrations of gaseous oxygen causes atelectasis, or lung collapse.
Other methods and processes have been developed to improve oxygen delivery to tissues. For instance, hyperbaric breathing chambers involve the placement of a person inside a sealed chamber with the subsequent pressurization of the chamber. During chamber pressurization, the patient inhales gaseous oxygen through normal respiratory channels which results in increased blood oxygen levels. However, multiple limitations exist for this method of oxygen therapy. For example, the breathing chambers are extremely expensive and complex facilities, and highly trained personnel are needed for safe operation. Further, the increased blood oxygen levels achieved during chamber pressurization and oxygen inhalation are lost when the chamber is de-pressurized and the person is removed from the chamber. Numerous complications have been documented with this method of oxygen therapy, including fires, explosions, oxygen toxicity, gas embolism, and Caisson's disease from rapid chamber de-pressurization.
Another traditional method of delivering oxygen to tissues is via intravenous injection of gaseous oxygen. This method has been found to be extremely hazardous, as gas bubbles tend to coalesce in the veins and occlude smaller pulmonary arteries. The resulting gaseous pulmonary embolism causes a decreased pulmonary circulation, arterial hypoxemia, and systemic hypoxia. Due to the extreme hazards, this method of oxygen therapy is generally considered to have little, if any, practical utility.
Maintaining proper carbon dioxide levels in the human body is similarly important. It is not uncommon that a patient experiencing lower levels of oxygen simultaneously experiences heightened carbon dioxide levels. For example, carbon dioxide retention may occur with hypoxemia in patients suffering from chronic obstructive pulmonary disease (COPD). This can be especially problematic as one of the treatments for COPD is supplemental oxygen therapy, which can itself lead to heightened carbon dioxide levels.